Art of precipitating metals from cyanid solutions.



UNITED STATES PATENT OFFICE.

VVILL IAM J. SHARWOOD, 'OF BERKELEY, CALIFORNIA. ASSIGNOR OF ONE-HALF TOCHARLES W. MERRILL, OF LEAD, SOUTH DAKOTA;

ART OF PRESCIPITATIINGIMETALS FROM CYANID SOLUTIONS.-

n'o'. ssasso.

Specification of Letters Patent.

Patented Oct. 9, 1906.

Application filed February 24. I904. Serial No. 195,124.

9' '0 (11M whont it may concern;

Be it known that I, WILLIAM J. SHARWOOD,

a citizen of the United States, residing at Berkeley, in the county ofAlameda and State of California, have invented an Improvement in the Artof Precipitating Metals from Cyanid Solutions, of which the following isa specification.

My invention relates to an improvement in processes for extractingprecious metals from cyanid. solutions, and particularly solutionscontaining double cyanids of gold and silver.

In the conduct of the cyanid process of ore treatment the solutionsobtained, containing the double cyanid of gold or silver or of gold andsilver with one or more of the alkali metals, are almost invariablyalkaline in reaction, and the precipitation of precious metal from themhas generally been efl'ected by bringing them into contact with metalliczinc in a stage offine division, though electrical and other methodshave been used to some extent. Under these conditions consid erableamounts of zinc are of necessity taken into solu- 'rilice a portion ofthe dissolved values.

Moreover, any copper when. present in the solution largely fails toprecipitate, thereby acmunulating in the solutions and rendering inert aconsiderable amount of cyanogen. Now I have discovered that where thesolutions are first made neutral and then brought into contact with thezinc in a fine state of division that the amount of zinc dissolved bythe solution during the act of precipitation is greatly reduced and theprecipitation of gold, silver, and copper, or of any of these metalswhich may. occur in the solution, more perfect. In this manner theaddition of an excess of acid is avoided thereby diminishing the costand reducing he quantity of zinc passing into solution, as any excess ofeither acid or alkali increases: the quantity of Zinc dissolved.

To carry this improvement into effect, I allow the solution containingthe double cyanid of the preciousmetal to accumulate in a suitable vat Ithen agitate or stir it and add a suitable acid or acid salt in suchquantity as to neutralize the solution, so that it no longer reactsalkaline toward a suitable indicator, such as phenol-phthalein. It isthen brought into contact with metallic zinc, either by agitating withor causing it to flow through or over a quantity of metallic zinc or analloy of zinc in a state of fine divi-- sion. The gold, silver, and.copper or such of these metals as are resent are thereby precipitatedand can e recovered and separated from any undissolved zinc by wellknownmeans.

For the purpose of neutralization it is con venient to use eithercommercial sulfuric acid or acid sodium sulfate, this latter being acheap salt formed as a by-product in various chemical manufactures. Inorder to facilitate precipitation ofthe )recious metals from neutralsolutions as well as from those which are alkaline, the solution may beheated or the zinc di ped first into solutions of certain salts ofotlier metals.

On neutralizing in the manner described the cyanid solutions obtained inmetallurgical practice a precipitate is frequently in the solution, butalso renders available much of the cyanogen which was previously held incombination as double cyanid of copier. 1 I am aware that neutral cyanidsolutions have been treated by means-of zinc in order to precipitate theprecious metals contained inthem; but .I believe it to be new to firstrender alkaline solutions as nearly as possible neutral and then toeffect precipitation by means of material containing zinc in a finestate of division.

I claim as my invention 1. The process of extracting metals from cyanidsolutions, which consists in neutralizg Y i @WILEYBU ing said-solutionsand then-bringing them into contact with a material continuing a moreelectropositiv-e metal in a fine state-of division whereby the metalsare precipitated. The process of extracting metals from cyanidsolutions, which consists in neutralizing said solutions by the additionof asuitable acid. containing matcrial'in iroper proortions, and, thenbringing suc solutions into contact with a material containing a moreelectropositive metal in a fine state of division whereby the metals areprecipitated.

The process of extracting precious metals and copper from cyanidsolutions, which consists in neutralizing said solutions, and thenbringing them into contact with material containing metallic zinc in astate of fine division,,while said solutions are neutral reaction,whereby the precious metals and copper are precipitated.

'4. The process of extracting precious metals and copper from alkalinedouble-cyanid solutions, which consists in rendering said solutionsneutral by the addition of a suitable acid-containing material, inproper proportions, and then bringing said solutions into contact withmaterial containing metallic tral by the addition of a suitableacid-eontaining material, in proper proportions, and

then bringing said solutions into contactwith an alloy of zinc, in astate of fine divi sion, whereby the precious metals and copper areprecipitated.

WM. J. SHARWOOD. Witnesses: v

EDMUND ONEILL, W. C. BLASDALE.

